Compact actuator

ABSTRACT

An actuator including a housing accommodating a screw mechanism and a drive including a motor. The screw mechanism includes a nut and a screw, one of which is rotatably supported with respect to the housing. Upon relative rotation of the nut and the screw, linear movement of one of the nut and the screw is obtained. At least a rotatable component of the drive, for example, the rotor of the motor, is rotatably supported on the screw which is rotatably supported with respect to the housing.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention is related to an actuator, comprising a housing whichcontains a screw mechanism and a motor, said screw mechanism comprisinga nut and a screw, one of which is rotatably supported with respect tothe housing, such that upon relative rotation of the nut and the screw alinear movement of one of said nut and screw is obtained.

2. Description of Related Art

In certain applications, such as actuators for disc brakes, clutchesetcetera, it is desirable to limit the overall dimensions and possiblythe weight as much as possible. According to the invention, a compactlayout may be obtained in that at least a rotatable component of thedrive, e.g. the rotor of the motor, is rotatably supported on the screwwhich is rotatably supported with respect to the housing.

In particular, in case the screw is rotatably supported with respect tothe housing by means of a support bearing, the screw may be integratedwith the outer ring of the support bearing, such that the rotor of themotor, by means of an auxiliary bearing, is rotatably supported on theouter ring of the support bearing.

The support bearing is preferably accommodated with the auxiliarybearing. In such embodiment, a compact and stiff support for the rotorand screw is obtained.

The linear movement provided by the actuator usually generates a force,e.g. in the case of a disc brake for clamping the brake pads onto thebrake disc.

As a result of the inevitable flexibility of the actuator and the systemto which said actuator is connected, elastic deformations are alsogenerated.

In so far as these deformations are axial-symmetric with respect to thescrew mechanism, no problems occur as to the proper function of theactuator. However, in certain cases, and in particular in the case ofdisc brakes, loads are generated which are eccentric with respect to theactuator.

The eccentricity is to be attributed to the asymmetric shape of thebrake calliper, in particular of the claw piece thereof which carriesthe brake pads and which accommodates the brake disc sideways.

Upon pressing the brake pads onto the brake disc, the claw piece isloaded in bending, which bending action is also transferred onto thehousing of the actuator. As the screw mechanism is supported within thehousing, said mechanism may become exposed to bending as well.

The screw mechanism is however rather vulnerable with respect tomisaligned forces, in such a way that the proper function may behampered and that damage may occur.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide an actuator of thetype described before, which is less vulnerable with respect tomisaligned forces. This object is achieved in that the screw mechanismis supported with respect to the housing by means of a joint whichallows rotations about at least one axis transverse with respect to saidlinear movement.

In case the housing of the actuator is loaded in bending, said bendingaction is relieved as a result of the freedom of the screw mechanism torotate around the transverse axis or axes. Thus, the screw mechanismwill not be exposed to misaligned forces.

In particular, one of the nut and screw is rotatably supported bothaccording to an axis parallel with respect to said linear movement, andaccording to at least one axis transverse with respect to said linearmovement. Said transverse rotation may be obtained by means of a balljoint.

Said ball joint may be situated at one end of a central support shaft,the other end of which is connected to the housing. According to apreferred embodiment, said ball joint may be connected to a supportbearing supporting one of the nut and the screw, said one of the nut andthe screw being drivably connected to the rotor of the motor.

The motor, preferably an electric motor, may engage the screw mechanismin several different ways. Usually, said motor is also connected to thehousing, which means that the connection between the motor and the screwmechanism is also exposed to the elastic bending action of the housingunder brake load.

Misalignment can be avoided here in case the nut and the screw engagesthe rotor through a coupling which allows rotations about at least oneaxis transverse with relation to the linear movement.

Said coupling may comprise an internally toothed member as well as anexternally toothed member having equal number of teeth. The bendingaction of the housing can be accommodated in particular in case theteeth of the externally toothed member are convexly curved in across-section parallel to the linear movement, and in case the teeth ofthe externally toothed member are centered with respect to the balljoint.

A compact embodiment is obtained in case the outer ring of the bearingis integrated with an internally toothed member. The screw and theinternally toothed member are at axially opposite ends of the outerring.

Conveniently, the rotor of the motor is rotatably supported on the outerring of the support bearing.

According to a first embodiment, the rotor engages an externally toothedmember through a reduction gear mechanism. Preferably, the supportbearing is supported on one end of a support shaft, the other end ofwhich is connected to the housing, the externally toothed member beingrotatably supported on said support shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the embodimentsshown in the figures.

FIG. 1 shows a first embodiment in longitudinal section.

FIG. 2 shows an exploded view of the embodiment according to FIG. 1.

FIG. 3 shows a second embodiment.

FIG. 4 shows a third embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The actuator shown in FIGS. 1 and 2 comprises a housing 1 containing ascrew mechanism 2 and a motor 3. Said screw mechanism 2 comprises a nut4 and a screw 5, provided with screw threads 6, 7 and which engage eachother by means of a number of balls 8. At the location of the inserts 9,the balls are transferred between adjacent windings of the screw threads6, 7.

The screw 5 is integrated with the outer ring 10 of support bearing 11.The outer ring 10 has a larger diameter than the screw 5, for reasons ofcompactness of the actuator.

The inner ring 12 of the support bearing 11 is integrated with a balljoint 13. In particular, the inner ring has a spherical inner surface14, which engages a ball 15 connected to the central support shaft 16.

Although the ball 15 is depicted as a separate part, it may also becarried out in one piece with the central support shaft 16. The centralsupport shaft 16 is connected to the housing through the clip ringarrangement 17, and load cell 18 for measuring axial forces.

The rotor 19 of the motor 3 is supported with respect to the outer ringof the support bearing 11 by means of a sleeve 31 having integratedbearings 20. Said sleeve 31 is fixed to the stator 21. The stator 21 ofthe motor 3 is fixably connected to the housing 1. Furthermore, thesleeve 31 is fixed to sleeve 32 of a reduction gear wheel mechanism 22.

By means of the reduction gear wheel mechanism 22, the motor 3 drivesthe sleeve 23, which carries an outwardly toothed member. This outwardlytooth member has teeth 25, which have a curved shape.

The outer ring 10 of the support bearing 11 carries an inwardly toothedmember 26, which carries inwardly directed teeth with a correspondinglycurved shape.

The number of outwardly directed teeth 25 and inwardly directed teeth 27is equal. These teeth engage each other so as to transfer the drivingaction from the sleeve 23 onto the screw 5.

The nut 4 is carried out as a piston which is slidably held in acylindrical space 28 in the housing 1. By means of pin 29 and groove 30in the cylinder, said cylinder is held axially movable, butnon-rotatable within the cylinder space 28.

Upon actuating the screw 5, the nut is therefore driven linearly and inaxial direction with respect to the housing 1, e.g. for driving thebrake pads of a brake calliper (not shown) towards and from each other.

In case, as a result of the forces generated in the housing 1, e.g. thehousing of a brake calliper, a flexible bending is imposed thereon, thescrew mechanism 2 is still protected against such loadings. Generally,screw mechanisms have a poor resistance against bending action, and thescrew mechanism 2 in question is relieved from any bending loads due tothe ball joint 13.

Also, the driving connection between motor 3 and screw mechanism 2 isrelieved from any bending loads due to the teeth drive of the inwardlytooth member 26 and the outwardly tooth member 24, and the curved shapeof the teeth in question. The embodiment of FIG. 3 shows a brakecalliper 40, comprising a housing 1 connected to claw piece 41 by meansof screw thread. At its side facing the actuator 1, the claw piece 41has a cavity 43 in which part of the stator 21 of motor 3 has beenaccommodated. Thereby, a very compact brake calliper 40 is obtained.

As usual, the claw piece 41 has a fixed brake pad 44 as well as amovable brake pad 45 which is connected to the nut 5 of the screwmechanism 2, in particular to the head 46 thereof.

Between the brake pads 44, 45, a brake disc 47 is accommodated. Thesupport shaft 16 supports the support bearing 11, the inner ring 12thereof being fixedly connected by means of e.g. a clip ring 48.

In this embodiment, the inner ring 12 of support bearing 11 has a closedhead 49, such that a load cell 50 can be accommodated between saidclosed head 49 and the facing end of support shaft 16.

The other components of this embodiment are to a large extend identicalto the embodiment of FIGS. 1 and 2.

In the embodiment of FIG. 4, it is shown that the external teeth 25 ofthe externally toothed member 24 are rounded off in longitudinalcross-section, so as to better allow bending deformations of thehousing, without however transferring the bending action onto the screwmechanism 2.

A grease-dosing unit 53 is accommodated in the base of the screw 5.

1. An actuator, comprising: a housing accommodating a screw mechanism;and a drive comprising a motor, wherein said screw mechanism comprises anut and a screw, of which the screw is rotatably supported relative tothe housing, such that upon relative rotation of the nut and the screw,a linear movement of said nut is obtained, wherein at least a rotatablecomponent of the drive is rotatably supported with respect to the screwwhich is rotatably supported relative to the housing, and the rotatablecomponent of the drive is a rotor of the motor, said rotor being coaxialwith respect to the screw.
 2. The actuator according to claim 1, whereinthe screw is rotatably supported with respect to the housing by asupport bearing.
 3. The actuator according to claim 2, wherein the rotorof the motor is rotatably supported on the screw by an auxiliarybearing.
 4. The actuator according to claim 3, wherein the supportbearing is accommodated within the auxiliary bearing.
 5. The actuatoraccording to claim 2, wherein the screw is integrated with an outer ringof the support bearing.
 6. The actuator according to claim 5, wherein anouter diameter of the outer ring of the support bearing is larger thanan outer diameter of the screw.
 7. The actuator according to claim 2,wherein an outer ring of the support bearing supports a rotatable sleevewhich is in connection with the rotatable component of the drive.
 8. Theactuator according to claim 7, wherein the sleeve is rotatably connectedto an outer ring of an auxiliary bearing which in turn is rotatablyconnected to an inner ring of the outer ring of the support bearing. 9.The actuator according to claim 8, wherein an inner surface of thesleeve comprises two axially spaced raceways, each of said racewaysengaging a number of rolling elements which each engage a raceway on anouter surface of the outer ring of the support bearing.
 10. The actuatoraccording to claim 7, wherein the sleeve is connected to the rotor ofthe motor.
 11. The actuator according to claim 1, wherein the screw isrotatably supported according to an axis parallel with respect to saidlinear movement, and according to at least one axis transverse withrespect to said linear movement.
 12. The actuator according to claim 11,the screw is supported with respect to the housing by a ball joint. 13.The actuator according to claim 12, wherein the ball joint is at one endof a central support shaft, and the other end of the central supportshaft is connected to the housing.
 14. The actuator according to claim13, wherein the ball joint is connected to a support bearing, saidsupport bearing supporting the screw, wherein said one of the nut andthe screw is drivably connected to the rotor of the motor.
 15. Theactuator according to claim 14, wherein the screw engages the rotorthrough a coupling which allows rotation about at least one axistransverse relative to the linear movement.
 16. The actuator accordingto claim 15, wherein a coupling comprises an internally toothed memberand an externally toothed member having an equal number of teeth. 17.The actuator according to claim 16, wherein the teeth of the externallytoothed member are convexly curved in a cross-section parallel to thelinear movement.
 18. The actuator according to claim 16, wherein theteeth of the externally toothed member are centered with respect to theball joint.
 19. The actuator according to claim 14, wherein the screw isintegrated with an outer ring of the support bearing.
 20. The actuatoraccording to claim 19, wherein an outer diameter of the outer ring ofthe support bearing is larger than an outer diameter of the screw. 21.The actuator according to claim 19, wherein the outer ring of thesupport bearing is integrated with an internally toothed member.
 22. Theactuator according to claim 20, wherein the screw and an internallytoothed member are at axially opposite ends of the outer ring of thesupport bearing.
 23. The actuator according to claim 19, wherein therotor of the motor is rotatably supported on the outer ring of thesupport bearing.
 24. The actuator according to claim 23, wherein therotor engages an externally toothed member through a reduction gearmechanism.
 25. The actuator according to claim 24, wherein the supportbearing is supported on one end of a support shaft, the other end of thesupport shaft is connected to the housing, the externally toothed memberbeing rotatably supported on said support shaft.
 26. The actuatoraccording to claim 19, wherein the rotor of the motor directly engagesthe outer ring of the support bearing.
 27. The actuator according toclaim 26, wherein the rotor is integrated with an internally toothedmember, and the outer ring of the support bearing is integrated with anexternally toothed member, said members engaging each other.
 28. Theactuator according to claim 13, wherein the screw and the support shafteach have a through going bore respectively, said bores being alignedwith each other.
 29. The actuator according to claim 1, wherein thescrew includes a bore containing a grease dosing unit.
 30. The actuatoraccording to claim 1, wherein at least one of the screw mechanism, asupport bearing, an auxiliary bearing and a reduction gear mechanismcomprises a surface obtained by hard turning.
 31. The actuator accordingto claim 1, wherein at least one of the screw mechanism, a supportbearing, an auxiliary bearing and a reduction gear mechanism comprises adiamond-like carbon coating.
 32. The actuator according to claim 1,wherein an encoder is provided for measuring a relative rotation.
 33. Abrake calliper for a disc brake, comprising: a claw piece carrying atleast two opposite brake pads which enclose a gap for accommodating thedisk brake; and an actuator, wherein said actuator comprises: a housingaccommodating a screw mechanism; and a drive comprising a motor, whereinsaid screw mechanism comprises a nut and a screw, of which the screw isrotatably supported relative to the housing, such that upon relativerotation of the nut and the screw, a linear movement of said nut isobtained, said housing being connected to the claw piece, wherein atleast a rotatable component of the drive is rotatably supported withrespect to the screw which is rotatably supported relative to thehousing, and wherein the rotatable component of the drive is a rotor ofthe motor, said rotor being coaxial with respect to the screw.